<script id="draw-shader-vs" type="x-shader/x-vertex">
precision mediump float;

attribute vec3 inPos;
attribute vec3 inCol;

varying   vec3 vertCol;

uniform   mat4 u_projectionMat44;
uniform   mat4 u_viewMat44;
uniform   mat4 u_modelMat44;

void main()
{
    vertCol       = inCol;
    vec4 modelPos = u_modelMat44 * vec4( inPos, 1.0 );
    vec4 viewPos  = u_viewMat44 * modelPos;
    gl_Position   = u_projectionMat44 * viewPos;
}
</script>

<script id="depth-shader-fs" type="x-shader/x-fragment">
precision mediump float;

varying vec3 vertCol;

void main()
{
    gl_FragColor = vec4( vertCol, 1.0 );
}
</script>

<style>
html,body { margin: 0; overflow: hidden; }
#gui { position : absolute; top : 0; left : 0; font-size : large; }
#ref-link { position : absolute; bottom : 0; left : 0; font-size : large; }  
</style>

<body>

<form id="gui" name="inputs">
    <table>
        <tr> <td> <font color= #CCF>field of view angle</font> </td> 
             <td> <input type="range" id="fov_input" min="30" max="150" value="90"/></td> </tr>
        <tr> <td> <font color=#CCF>animate view</font> </td> 
             <td> <input type="checkbox" id="chg_view" checked="1" /></td></tr> 
        <tr> <td> <font color=#CCF>rotate model</font> </td> 
             <td> <input type="checkbox" id="rot_model" checked="1" /></td></tr>     
        <tr> <td> <font color= #CCF><span id="fov">0</span></font> </td> </tr>
        <tr> <td> <font color= #CCF><span id="view_x">0</span></font> </td> </tr>
        <tr> <td> <font color= #CCF><span id="view_y">0</span></font> </td> </tr>
        <tr> <td> <font color= #CCF><span id="view_z">0</span></font> </td> </tr>
    </table>
</form> 

<canvas id="camera-canvas" style="border: none"></canvas>
</body>

<script type="text/javascript">

(function loadscene() {

var gl, canvas, vp_size, prog, bufObj = {};

function render(deltaMS) {

    var fov_val = parseInt(document.getElementById( "fov_input" ).value);
    var chg_view = document.getElementById( "chg_view" ).checked;
    var rot_model = document.getElementById( "rot_model" ).checked;

    Camera.create();
    Camera.fov_y = fov_val;
    Camera.vp = [canvas.width, canvas.height];
    if ( chg_view )
      Camera.pos = EllipticalPosition( 7, 4, CalcAng( deltaMS, 10.0 ) );

    document.getElementById( "fov" ).innerHTML = "filed of view (y axis, degrees): " + (fov_val<100 ? "0" : "") + fov_val + "°";
    document.getElementById( "view_x" ).innerHTML = "view position x: " + Camera.pos[0].toFixed(5);
    document.getElementById( "view_y" ).innerHTML = "view position y: " + Camera.pos[1].toFixed(5); 
    document.getElementById( "view_z" ).innerHTML = "view position z: " + Camera.pos[2].toFixed(5); 

    var prj_mat = Camera.Perspective();
    var view_mat = Camera.LookAt();
    var model_mat = IdentM44();
    if ( rot_model ) {
        model_mat = RotateAxis( model_mat, CalcAng(deltaMS, 17.0), 0 );
        model_mat = RotateAxis( model_mat, CalcAng(deltaMS, 13.0), 1 );
    }
        
    gl.viewport( 0, 0, canvas.width, canvas.height );
    gl.enable( gl.DEPTH_TEST );
    gl.clearColor( 0.0, 0.0, 0.0, 1.0 );
    gl.clear( gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT );
    ShProg.Use( progDraw );
    ShProg.SetM44( progDraw, "u_projectionMat44", prj_mat );
    ShProg.SetM44( progDraw, "u_viewMat44", view_mat );
    ShProg.SetM44( progDraw, "u_modelMat44", model_mat );
    VertexBuffer.Draw( bufObj );

    requestAnimationFrame(render);
}

function initScene() {

    canvas = document.getElementById( "camera-canvas");
    vp_size = [canvas.width, canvas.height];
    gl = canvas.getContext( "experimental-webgl" );
    if ( !gl )
      return;

    progDraw = ShProg.Create( 
      [ { source : "draw-shader-vs", stage : gl.VERTEX_SHADER },
        { source : "depth-shader-fs", stage : gl.FRAGMENT_SHADER }
      ] );
    progDraw.inPos = gl.getAttribLocation( progDraw.progObj, "inPos" );
    progDraw.inCol = gl.getAttribLocation( progDraw.progObj, "inCol" );
    if ( progDraw.progObj == 0 )
        return;

    var sin120 = 0.8660254
    var pos = [ 0.0, 0.0, 1.0, 0.0, -sin120, -0.5, sin120 * sin120, 0.5 * sin120, -0.5, -sin120 * sin120, 0.5 * sin120, -0.5 ];
    var col = [ 1.0, 0.0, 0.0, 1.0, 1.0, 0.0, 0.0, 0.0, 1.0, 0.0, 1.0, 0.0 ];
    var inx = [ 0, 1, 2, 0, 2, 3, 0, 3, 1, 1, 3, 2 ];
    bufObj = VertexBuffer.Create(
      [ { data : pos, attrSize : 3, attrLoc : progDraw.inPos },
        { data : col, attrSize : 3, attrLoc : progDraw.inCol } ],
        inx );

    window.onresize = resize;
    resize();
    requestAnimationFrame(render);
}

function resize() {
    //vp_size = [gl.drawingBufferWidth, gl.drawingBufferHeight];
    vp_size = [window.innerWidth, window.innerHeight];
    //vp_size = [256, 256]
    canvas.width = vp_size[0];
    canvas.height = vp_size[1];
}

function IdentM44() { return [1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1]; }

function RotateAxis(matA, angRad, axis) {
    var aMap = [ [1, 2], [2, 0], [0, 1] ];
    var a0 = aMap[axis][0], a1 = aMap[axis][1]; 
    var sinAng = Math.sin(angRad), cosAng = Math.cos(angRad);
    var matB = matA.slice(0);
    for ( var i = 0; i < 3; ++ i ) {
        matB[a0*4+i] = matA[a0*4+i] * cosAng + matA[a1*4+i] * sinAng;
        matB[a1*4+i] = matA[a0*4+i] * -sinAng + matA[a1*4+i] * cosAng;
    }
    return matB;
}

function Cross( a, b ) { return [ a[1] * b[2] - a[2] * b[1], a[2] * b[0] - a[0] * b[2], a[0] * b[1] - a[1] * b[0], 0.0 ]; }
function Dot( a, b ) { return a[0]*b[0] + a[1]*b[1] + a[2]*b[2]; }
function Normalize( v ) {
    var len = Math.sqrt( v[0] * v[0] + v[1] * v[1] + v[2] * v[2] );
    return [ v[0] / len, v[1] / len, v[2] / len ];
}

var Camera = {};
Camera.create = function() {
    this.pos    = [0, 3, 0];
    this.target = [0, 0, 0];
    this.up     = [0, 0, 1];
    this.fov_y  = 90;
    this.vp     = [800, 600];
    this.near   = 0.1;
    this.far    = 100.0;
}
Camera.Perspective = function() {
    var fn = this.far + this.near;
    var f_n = this.far - this.near;
    var r = this.vp[0] / this.vp[1];
    var t = 1 / Math.tan( Math.PI * this.fov_y / 360 );
    var m = IdentM44();
    m[0]  = t/r; m[1]  = 0; m[2]  =  0;                              m[3]  = 0;
    m[4]  = 0;   m[5]  = t; m[6]  =  0;                              m[7]  = 0;
    m[8]  = 0;   m[9]  = 0; m[10] = -fn / f_n;                       m[11] = -1;
    m[12] = 0;   m[13] = 0; m[14] = -2 * this.far * this.near / f_n; m[15] =  0;
    return m;
}
Camera.LookAt = function() {
    var mz = Normalize( [ this.pos[0]-this.target[0], this.pos[1]-this.target[1], this.pos[2]-this.target[2] ] );
    var mx = Normalize( Cross( this.up, mz ) );
    var my = Normalize( Cross( mz, mx ) );
    var tx = Dot( mx, this.pos );
    var ty = Dot( my, this.pos );
    var tz = Dot( [-mz[0], -mz[1], -mz[2]], this.pos ); 
    var m = IdentM44();
    m[0]  = mx[0]; m[1]  = my[0]; m[2]  = mz[0]; m[3]  = 0;
    m[4]  = mx[1]; m[5]  = my[1]; m[6]  = mz[1]; m[7]  = 0;
    m[8]  = mx[2]; m[9]  = my[2]; m[10] = mz[2]; m[11] = 0;
    m[12] = tx;    m[13] = ty;    m[14] = tz;    m[15] = 1; 
    return m;
} 

var ShProg = {
Create: function (shaderList) {
    var shaderObjs = [];
    for (var i_sh = 0; i_sh < shaderList.length; ++i_sh) {
        var shderObj = this.Compile(shaderList[i_sh].source, shaderList[i_sh].stage);
        if (shderObj) shaderObjs.push(shderObj);
    }
    var prog = {}
    prog.progObj = this.Link(shaderObjs)
    if (prog.progObj) {
        prog.attrInx = {};
        var noOfAttributes = gl.getProgramParameter(prog.progObj, gl.ACTIVE_ATTRIBUTES);
        for (var i_n = 0; i_n < noOfAttributes; ++i_n) {
            var name = gl.getActiveAttrib(prog.progObj, i_n).name;
            prog.attrInx[name] = gl.getAttribLocation(prog.progObj, name);
        }
        prog.uniLoc = {};
        var noOfUniforms = gl.getProgramParameter(prog.progObj, gl.ACTIVE_UNIFORMS);
        for (var i_n = 0; i_n < noOfUniforms; ++i_n) {
            var name = gl.getActiveUniform(prog.progObj, i_n).name;
            prog.uniLoc[name] = gl.getUniformLocation(prog.progObj, name);
        }
    }
    return prog;
},
AttrI: function (prog, name) { return prog.attrInx[name]; },
UniformL: function (prog, name) { return prog.uniLoc[name]; },
Use: function (prog) { gl.useProgram(prog.progObj); },
SetI1: function (prog, name, val) { if (prog.uniLoc[name]) gl.uniform1i(prog.uniLoc[name], val); },
SetF1: function (prog, name, val) { if (prog.uniLoc[name]) gl.uniform1f(prog.uniLoc[name], val); },
SetF2: function (prog, name, arr) { if (prog.uniLoc[name]) gl.uniform2fv(prog.uniLoc[name], arr); },
SetF3: function (prog, name, arr) { if (prog.uniLoc[name]) gl.uniform3fv(prog.uniLoc[name], arr); },
SetF4: function (prog, name, arr) { if (prog.uniLoc[name]) gl.uniform4fv(prog.uniLoc[name], arr); },
SetM33: function (prog, name, mat) { if (prog.uniLoc[name]) gl.uniformMatrix3fv(prog.uniLoc[name], false, mat); },
SetM44: function (prog, name, mat) { if (prog.uniLoc[name]) gl.uniformMatrix4fv(prog.uniLoc[name], false, mat); },
Compile: function (source, shaderStage) {
    var shaderScript = document.getElementById(source);
    if (shaderScript)
        source = shaderScript.text;
    var shaderObj = gl.createShader(shaderStage);
    gl.shaderSource(shaderObj, source);
    gl.compileShader(shaderObj);
    var status = gl.getShaderParameter(shaderObj, gl.COMPILE_STATUS);
    if (!status) alert(gl.getShaderInfoLog(shaderObj));
    return status ? shaderObj : null;
},
Link: function (shaderObjs) {
    var prog = gl.createProgram();
    for (var i_sh = 0; i_sh < shaderObjs.length; ++i_sh)
        gl.attachShader(prog, shaderObjs[i_sh]);
    gl.linkProgram(prog);
    status = gl.getProgramParameter(prog, gl.LINK_STATUS);
    if ( !status ) alert(gl.getProgramInfoLog(prog));
    return status ? prog : null;
} };
        
function Fract( val ) { 
    return val - Math.trunc( val );
}
function CalcAng( deltaMS, interval ) {
    return Fract( deltaMS / (1000*interval) ) * 2.0 * Math.PI;
}
function CalcMove( deltaMS, interval, range ) {
    var pos = self.Fract( deltaMS / (1000*interval) ) * 2.0
    var pos = pos < 1.0 ? pos : (2.0-pos)
    return range[0] + (range[1] - range[0]) * pos;
}    
function EllipticalPosition( a, b, angRag ) {
    var a_b = a * a - b * b
    var ea = (a_b <= 0) ? 0 : Math.sqrt( a_b );
    var eb = (a_b >= 0) ? 0 : Math.sqrt( -a_b );
    return [ a * Math.sin( angRag ) - ea, b * Math.cos( angRag ) - eb, 0 ];
}

var VertexBuffer = {
Create: function(attribs, indices, type) {
    var buffer = { buf: [], attr: [], inx: gl.createBuffer(), inxLen: indices.length, primitive_type: type ? type : gl.TRIANGLES };
    for (var i=0; i<attribs.length; ++i) {
        buffer.buf.push(gl.createBuffer());
        buffer.attr.push({ size : attribs[i].attrSize, loc : attribs[i].attrLoc, no_of: attribs[i].data.length/attribs[i].attrSize });
        gl.bindBuffer(gl.ARRAY_BUFFER, buffer.buf[i]);
        gl.bufferData(gl.ARRAY_BUFFER, new Float32Array( attribs[i].data ), gl.STATIC_DRAW);
    }
    gl.bindBuffer(gl.ARRAY_BUFFER, null);
    if ( buffer.inxLen > 0 ) {
        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, buffer.inx);
        gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array( indices ), gl.STATIC_DRAW);
        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);
    }
    return buffer;
},
Draw: function(bufObj) {
    for (var i=0; i<bufObj.buf.length; ++i) {
        gl.bindBuffer(gl.ARRAY_BUFFER, bufObj.buf[i]);
        gl.vertexAttribPointer(bufObj.attr[i].loc, bufObj.attr[i].size, gl.FLOAT, false, 0, 0);
        gl.enableVertexAttribArray( bufObj.attr[i].loc);
    }
    if ( bufObj.inxLen > 0 ) {
        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, bufObj.inx);
        gl.drawElements(bufObj.primitive_type, bufObj.inxLen, gl.UNSIGNED_SHORT, 0);
        gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, null );
    }
    else
        gl.drawArrays(bufObj.primitive_type, 0, bufObj.attr[0].no_of );
    for (var i=0; i<bufObj.buf.length; ++i)
        gl.disableVertexAttribArray(bufObj.attr[i].loc);
    gl.bindBuffer( gl.ARRAY_BUFFER, null );
} };

initScene();

})(); 

</script>
